1. Field of the Invention
This invention generally relates to a slide fastener and more particularly, to a coupling element for a slide fastener and a method of making the same.
2. Prior Art
In manufacturing fastener coupling elements of a discrete formation, it is one of the commonly employed techniques to stamp out flat blank sheet metal to a given configuration. The coupling elements thus produced have pairs of tape edge clamping legs of a substantially square cross section. A problem experienced with these prior art coupling elements is that the legs when pressed against an element-carrying tape edge for gripping engagement therewith, are unable to bite sufficiently deep into the tape edge due primarily to the wide tape gripping surfaces of the legs. The attached coupling elements are therefore susceptible to displacement from a proper position on the tape edge when subjected to repeated external stresses applied in the use of the slide fastener, resulting in disturbed pitches or distances between adjacent coupling elements and thus, in malfunctioning of the slide fastener. Another difficulty with the conventional coupling elements formed from flat blank sheet is that the coupling elements are subjected to varying stresses because interlocking engagement between the opposed coupling heads is much larger in strength than gripping engagement of the element legs with the tape edges.
Furthermore, the use of flat blank sheet metal is disadvantageous in that when stamping out the sheet metal, cutting blade and blade supporting parts are subjected to severe shock loads and a high rate of wear. Such wear is primarily induced by the impacting contact occurring at one time between the entire length of the cutting blade and the entire surface of the sheet metal during stamping operation. This has led to the drawback that the worn members need be replaced at short intervals of time and the production rate of the coupling elements becomes reduced due to frequent replacement of such members.